User manual

43
Serial Bus Analysis
❙ Read/Write bit (R/W): Indicates, if the data is to be written
or read out from the slave
❙ Acknowledge bit (ACK): Is issued by the recipient of the
previous byte if transmission was successful (exception:
for read access, the master terminates the data
transmission with a NACK bit after the last byte)
❙ Data: a series of data bytes with a ACK bit after each byte
❙ Stop condition: rising slope on SDA (Serial Data), while
SCL (Serial Clock) is HIGH
13.4.1 I
2
C BUS Conguration
To decode the I
2
C BUS it is necessary to determine du-
ringthebuscongurationwhichlogicchannelwillbe
connected to the clock (SCL) and which one to the data
line (SDA). This setting is selected after choosing the BUS
TYPE I
2
C in the BUS menu and pressing the soft menu
key CONFIGURATION. In the menu, choose the top soft
menu key CLOCK SCL and use the universal knob in the
CURSOR/MENU section to select the source channel. You
candenethedatachannelbypressingthesoftmenu
key DATA SDA. With the soft menu key 7BIT ADRESS you
can choose, if the adress should be interpretated inclusive
(ADR.+RW) or without Read/Write bit (ADDR. ONLY).
A small window provides information about the current
settings. Press the MENU OFF button twice to close all
menus.
Certain portions of the I
2
C messages will be displayed
in color to distinguish between the different elements.
If the data lines are selected with the table display, the
respective sections will also be displayed in color. These
are described as follows:
❙ Read address: Yellow
❙ Write address: Magenta
❙ Data: Cyan
❙ Start: White
❙ Stop: White
❙ No acknowledge: Red
❙ Acknowledge: Green
13.4.2 I
2
C Bus Triggering
After the BUSconguration,itwillbepossibletotrigger
on various events. Press the TYPE button in the TRIGGER
section and choose the soft menu key SERIAL BUSES.
Then press the SOURCE button in the TRIGGER section
and choose I
2
C Bus. This will only be available if it was
conguredearlier.PresstheFILTERbuttonintheTRIGGER
section to list all available I
2
C trigger conditions.
Following triggerconditionscanbedened:
Prior to the BUS conguration it is necessary to set the correct
logic level (threshold). Please refer to chapter 4.5. The default
setting is 500 mV.
If the option HOO11 resp. the voucher HV111 is installed, it it only
possible to select analog channels as source. If the option HOO10
resp. the voucher HV110 is installed, both analog and digital
channels are available as source.
❙ START: The oscilloscope triggers on the frame start
sequence.The start sequence is the falling slope on SDA
when SCL is high.
❙ STOP: The oscilloscope triggers on the frame stop
sequence. The start signal is the rising slope on SDA
when SCL is high.
❙ RESTART: The oscilloscope triggers, if a new start
sequence occurs before the stop condition. The new start
signal is a repeated start signal.
❙ NOT-ACKNOWLEDGE: The NOT-ACKNOWLEDGE bit is
the 9th bit in a data or address unit of the SDA line. For
NOT-ACKNOWLEDGE, the Acknowledge bit is on SDA
high, although it should be low.
❙ READ/WRITE: The soft menu key READ/WRITE offers
additional trigger options. You can use the soft menu key
MASTER to toggle the trigger condition between read and
writeaccess.The8thbitoftherstdataunit(depending
on the address length) is used to distinguish between
read and write access. The selected condition is displayed
in the I
2
C settings window and is highlighted by the menu
key in blue. Theaddresslength(inbit)denesthe
maximum number of slave addresses to be used with the
bus. For a 7 bit address length, the maximum number of
available addresses is 112. The 10 bit addressing mode is
downward compatible with the 7 bit addressing mode by
using 4 of 16 reserved addresses and can be used
simultaneously. For a 10 bit address length, a total of
1136 addresses (1024 + 128 - 16) is available. The highest
10 bit address is 1023 (0x3FF). The selected address
length is displayed in the I
2
C settings window and is high-
lighted by the menu key in blue. The SLAVE ADDRESS is
the address used on the BUS to distinguish which slave
the master communicates with. Use the universal knob in
the CURSOR/MENU section to select the address for the
observing bus participant to be triggered. The soft menu
DATAenablesyoutoenterspecicdatainadditiontothe
address. With this menu, you can trigger on clearly
deneddatabytes(colorcyan)withinthetransmission,
allowingyoutolteroutirrelevanttransmissions.Youcan
trigger on up to 24 bit (3 byte) of data. An offset of 0 to
4095 to the address is allowed. Select BYTE OFFSET
whichdenesthedistancebetweenthebytesrelevant
Fig. 13.4: I
2
C Read/Wrtie trigger menu